Coated cellulosic film



April 28, 1942. w. J. JEBENs COATED CELLULOSIG FILM Filed Sept. l, 1939MSN Il l l /wmmw NVM@ ATTORNEY Patented Apr. 28, 1942 COATED CELLULOSICFILM Walter John Jebens, Kenmore, N. Y., assigner to E. I. du Pont deNemours & Company, Wilmlngton, Del., a' corporation of DelawareApplication September 1, 1939, Serial No. 293,056

6 Claims.

This invention relates to moistureproof sheet wrapping material, andmore particularly to the moistureproofing of regenerated cellulose andlike film. It especially appertains to the anchoring of moisturepr-oofcoatings to the base sheet.

Recently there has appeared in commerce a transparent moistureproofsheet Wrapping material'consisting of a base sheet of regeneratedcellulose film coated with a moistureproofing coating composition. Whenproducts containing considerable water (cheese, iish, fresh vegetables,etc.) are wrapped in such material, the surface coating loosens in a fewhours. As a result, the eil'ectiveness of the wrapping is veryappreciably reduced. Among the various plans which have been proposedfor avoiding or overcoming this failing is that of anchoring themoistureproof coating to the base sheet by means of an intermediatecoat, In spite of the very great advance described in these patents,there is still considerable room for improvement.

It was an object of this invention to improve sheet wrapping materialshaving anchored moistureproot coatings. Another object was theproductionl of a iiexible, odorless, colorless, transparent,moistureproof sheet wrapping material comprising a regenerated cellulosefilm having a moistureproof coating adhering tenaciously thereto eveninthe presence of water. Further objects were to devise a simple processapplicable to existing and conventional equipment for anchoringmoistureproof coating lto regenerated cellulose and like film, toimprove the anchorage of moistureproof coatings comprising lilm former,a moistureproong agent, a blending agent and a plasticizer toregenerated cellulosic film, and to anchor a moistureproof coating to aregenerated cellulose film with a dimethylol urea ether l application.

type synthetic resin. A still further object was to compound thesub-coat of a moistureproof coated regenerated cellulose iilm from anormally tacky resin so that it would, upon deposition from solution,exude material reducing its tackiness to such an extent 'that rolling orstacking priorto the application of the adjacent coat is possible. Ageneral advance in the art and other objects which will appearhereinafter are also contem plated.

Surprisingly, it has now been found that an intermediate coating of anether derivative of a methylol urea Will securely adhere am-oistureproof coating to regenerated cellulose film, and that theresulting moistureproof sheet Wrapping material is greatly superior tothe products heretofore known.

From the following description and specific examples, in which aredisclosed certain embodiments of the invention as well as details ofwhat is believed to be the best mode for carrying out the invention, itwill be apparent'how the foregoing objects and related ends areaccomplished.

The written description is amplified by the accompanying drawing, inwhich:

Figure 1 is a sectional elevation view showing the manner of applyingthe anchoring coating;

Figure 2 is an isometric view of the base sheet material before theapplication of an anchoring coating; Y

Figure 3 is an isometric view showing the relation-0f the anchoringcoating and the base sheet; and v Figure 4 is an isometric view showingthe relation of the anchoring coating, the moistureproof coating and thebase sheet.

In Figures 2, 3 and 4 the thickness dimension is very greatlyexaggerated in the interest of clarity.

The parts are given by weight throughout the Example 1 l A web ofVregenerated cellulose in gel condition,

which had been cast from viscose, desulfured,.

bleached and washed free from impurities in the conventional manner wasled through an aqueous softening bath containing 4.33% glycerin. The geliilm containing the glycerinsoftener was then dried in the usual mannerby passage over heated rolls at temperatures of 90 C. 'I'he web was thenpassed through a solution consisting of: Per cent Di-iso-butyl ether ofdi-methylol urea 8.0 Citric acid- 1.5 Ethyl .alcoho1 90.5 The treatingbath was proportioned so that 30 pounds of the solution were associatedwith 100 I pounds of cellulose of 0.001 of an inch thickness. The coatedsheet was then dried by maintaining it at a temperature of C. 4until allthe solvent had been removed from the sheet and the dimethylol ureaether product had become hard, tack-free and substantially insoluble.

'I'he product employed as this anchoring intermediate or under-coat wasprepared by reacting dimethylol urea with isobutyl alcohol in thepresence of phthalic anhydride as a catalyst at a temperatureapproximating C. It was partially condensed (polymerized or hardened)and dehydrated before being applied to the regenerated cellulose sheet.

Where there is a tendency for the dimethylol urea ether product todeposit on the drier rolls, the web may first be given a preliminarypartial drying out of contact with any surface, as, for example, bypassing this sheet through air heated to an elevated temperature.

After bringing the coated sheet as produced above toa normal humidity,it was moistureproofed by passing it through a moistureproofing coatingcomposition of the following formula:

The excess of the coating material wasremoved by scraping, and thecoated sheet dried at a temperature above the melting point of the wax.The finished coated sheet was then again conditioned vto bring it to thedesired moisture content.

There resulted a moistureproofed sheet of regenerated cellulose which.was transparent, flexible, odorless and colorless. It retained itsmoistureproof surface coating tenaciously, even when in direct contactwith water and moisture for prolonged periods of time. It was admirablysuited for wrapping material to be employed in contact with productscontai'ning large amounts of water or moisture such as butter, cheese,wet fish, frozen fish, ice cream, and the like. The wrapping materialperformed itsdesired Vfunction as a wrapper for these materials evenwhen they were stored for appreciable periods of time.

` Example II The procedure of Example I was repeated, us-

ing a sub-coating composition consisting of:

This-solution was applied in such a Way that 10 pounds were associatedwith 100 pounds of cellulose.

Eample III The procedure of Example I was followed, using anintermediate anchoring coating'composition consisting of:

Per cent Dilauryl ether of dimethylol urea 12.0 Dewaxed shellac 4.0Tartaric acid 0.6 Ethyl alcohol 25.0 Ethyl acetate 58.4

This ethyl alcohol solution of the dilauryl ether of dimethylol urea wasapplied in such a way that 20 pounds of the solution was associated with100 pounds of cellulose.

Example IV A'web of regenerated cellulose in gel condition, which hadbeen cast from viscose, desulfured, bleached, washed free fromimpurities in the usual manner in the casting machine, and which wasready for a softening treatment, was led through an aqueous glycerolbath containing, in addition tov Ll1/a% by weight of glycerol (theamount of glycerol normallyused for softening regenerated cellulosefilm), 0.75% of dimethylol urea ether of ethyl alcohol and 0.08% ofcitric acid. The web of regenerated cellulose was in contact with thisaqueous solution for 10 to 20 seconds, after which the excess solutionwas removed from the sheet by means of squeeze rolls which reduced thewater content of the sheet to between three and four times the weight ofthe cellulose. The web, wet with the solution of anchoring material andglycerol, was then ready to be dried. During the drying (water removal),the resin forming materials reacted (under the influence of the heatemployed for the drying) to form a, substantially insoluble resin in oron the sheet. The drying was carried out according to the usual methodfor drying` regenerated cellulose sheeting on a casting machine, namely,by bringing the sheet directly from the squeeze rolls into contact withheated rolls and drying the sheet at a temperature of between 60 and 90C. A tendency for the substantially insoluble resin to be deposited onthe drier rolls as they become wet with the solution from the wetcellulosic web passing over them, may make it desirable to follow adifferent drying procedure in some cases. A deposit of resin may flakeoff from time to time on the fresh cellulosic sheeting passing over therolls, thereby imparting a faintly mottled-appearance to the dryingsheet.

In this example (which describes a preferred procedure), the regeneratedcellulose web, wet with the solution of polymerizable resin material andglycerol, after passing through the squeeze rolls and before coming intocontact with the drier rolls, was rst given a preliminary or partialdrying out of contact with any surface. This was accomplished by passingthe web through air heated to an elevated temperature by means of asuitable arrangement of gas burners (electric heaters have also beenused satisfactorily), whereby the moisture content of the sheet wasreduced to the desired extent, in this instance from one-third toone-half of the initial water content. The partially dried cellulosicsheet was then led over the .heated rolls of the casting machine in theusual manner to complete the drying operation and to complete theformation of the substantially insoluble ether in and/or on the sheet.

The resulting sheet of regenerated cellulose with its substantiallyinsoluble ether coating was then .rehumidied to ordinary normal moisturecontent and coated with a moistureproong coating having the composition:

Per cent 12.5% N2 nitrocellulose, 10" visc 6. '70 Parailin wax (M. P. 60C.) l5 Dibutyl phthalate 2. Damar 1. 50 Ethyl alcohol 2. 90 Acetone 1.'l5A Water 0. 30 Ethyl acetate 51. 00 Toluene 33. 10

The sheet was passed through the moistureproofing composition the excesscoating removed by scraping, and the coated sheet dried at a temperatureabove the melting point of the Wax. The finished coated sheet was thenagain conditioned to brins it to the desired moisture content. Theresulting product was a coated sheet of regenerated cellulose which wasinexpensive to produce, transparent, flexible, odorless andmoistureproof. The moistureproof surface coating adhered (was anchored)very tenaciously to the sheet and remained so for substantial periods of`time even when the sheet was in direct contact with water, dilute acidsand the like. It was very satisfactory as a wrapping in direct contactwith products containing large amounts of moisture or water such asbutter, cheese, wet or frozen fish, ice cream, or the like.

Ezample'V A softening anchoring coat bath, such as that described inExample IV, was prepared, using as4 the anchoring resin the dimethylolurea ether`- of ethylene glycol monomethyl ether. The procedure ofExample IV was then followed, using the new treating bath. The finalfilm exhibited was prepared and applied to a finished sheet ofregenerated cellulose by passing the sheet through the solution andremoving the excess solution by means of a suitable scraping mechanism.The coated sheet was then dried at a temperature of 100 moved from thesheet and the polymerized coating. The dried coating was about 0.0001 ofan inch in thickness. The nitrocellulose spewed forth as the solventevaporated, forming a superficial layer which was hard and tack-free.The coated sheet was rolled for storage purposes, and later coated witha moistureproofing coating composition in accordance with the procedureset out in Example IV.

The resulting moistureproofed sheet of regenerated cellulose wastransparent, flexible, odorless, colorless, and retained itsmoistureproof surface coating continuously even when in direct contactwith water or moisture for prolonged periods of time. It was Well suitedfor wrapping moisture-containing products such as butter,

cheese, frozen commodities, and the like.

Example VII The procedure ,of Example VI was followed, using a sub-coatcoating composition of the following formulation:

Per cent Urea formaldehyde monohydric alcohol (iso-butanol) resinsolution (55% soluformulation;

The procedure of Example VI was followed' using a sub-coat coatingcomposition of the following formulation:

Toluene Example IX The. procedure of Example VI was followed,

using asub-coat composition of the following Y Per .cent

I Ureav formaldehyde monohydric alcohol the desired anchorage for themoistureproof coat- C. until all the solvent had been resolution innormal-butanol) Ethanol (normal-butanol) resin solutiony (65%Nitrocellulose (2500 second) Maleic anhydride Isobutanol Tpluene Ethylacetate A web of regenerated cellulose which had been cast from viscose,desulfured, bleached, washed, softened by passage through a 6% aqueousglycerin bath and dried, all in the usual manner, was

, 'passed through a 11.7% solids coating composition. The solidsconsisted of Per cent Urea formaldehyde monohydric alcohol (iso-butanol)resinsolution (65% solution in isobutanol) 25.2 11.4% N nitrocellulose49.2 Dicyclohexyl 4phthalate 9.0 Dimethyl cyclohexyl phthalate 9.0Maleic acid 4.8 Paraflin wax 1.5 Damar resin 1.3

and the solvent consisted of ethyl acetate (46.0%), toluene (40.0%), andisobutyl alcohol (14.0%). The excess of the coating composition wasremoved by scraping, and the coated sheet dried at a temperature abovethe melting point of the Wax.

Example XI The procedure of Example X was carried out, using a coatingcomposition consisting of 65% solution in normalbutanol) 7.2 11.4%nitrogen nitrocotton 4.2 Parafn 0.6 Phthalic anhydride 0.48 Dewaxeddamar 1.2 Dibutyl phthalate 1.2 Ethyl acetate 57.20 Toluene 26.40 Ethylalcohol 1.52

As shown by the specific examples, the anchorage of a irioistureproofcoating on regenerated cellulose 'filmo is very greatly improved by thepresenceI of .a sub-coat comprising essentially polymerized derivativeof monoand/or dimethylol urea alkyl ether. The solids of the subr cent yvwhich accompany such a process). insoluble products may be applied inthe form coating composition may consist of the ether material, or, asin Examples VI, VII, VIII and IX, may comprise in addition 'a materialwhich will blush or exude uponV levaporation of the solvent. This exudedmaterial serves the purpose of drying the coating and rendering ittack-free when the coating has become hard upon evaporation of thesolvent therefrom. Preferably a blushed material soluble in themoistureproong coating composition is used. When this is done, theexudate becomes apart of the top coating, thereby preventing itsimpairing the clarity of the finished sheet material.

The ether type material may be applied to the lregenerated cellulosefilm in the monomeric and partially polymerized forms. In the lattercases the condensation or polymerization may be products areeconomically applied from an aqueous bath, as illustrated in Examples IVand V (this method is simple and .has the advantages The water of `anemulsion, orin solution inorganic liquids (solvents) Some of theproducts being soluble in both Water and common organic solvents may beapplied to thebase as a'solution in either One.

Ordinarily the moistureproof coating is not applied until the' sub-coathas reached a tackfree and substantially insoluble form.

The preparation of the urea formaldehyde lcompleted on the base sheet.The water soluble monohydric alcohol reaction product resin soluv tionsmay be carried out in various ways. Preferred procedures are describedin detail in British Patent 483,399, and United States Patent 2,191,957dated` February 27, 1940 (Edgar 8l Robinson) The methylol urea ethersmay be prepared according to the disclosures in United States Patents2,191,974, 2,201,927, 2,213,921 and 2,247,419.

The most satisfactory operatingprocedures: forl the application ofmethylol urea ethers from aqueous solutions are obtained whenl thepolymerization products are capable of rapid formation at temperaturesof under 200 C. (preferably capable of formation in 5 minutes or less at100 C. or less because of the inconvenience of operation and effect uponthe cellulosic sheet). In addition, the polymerization products shouldbe substantially insoluble in and unaffected by water and organicliquids (such `as those employed as solvents in the surface coatingcompositions), and formed by the reaction of substances which arethemselves sufficiently water soluble to yield aqueous solutions of thenecessary concentration.` Products substantially colorless, at least invery thin films (preferably less than 0.001 inch in thickness) are mostdesirable. Representative compounds in this group of materials are themethyl ether of mono-methylol urea, the ethyl ether of mono-methylolurea, the methyl ether of di-methylol urea, the ethyl ether ofdi-methylol urea, the methyl ether of mono-methylol thiourea, the ethylether of mono-methylol thiourea, the methyl ether of dimethylolthiourea, theethyl ether of di-methylol thiourea, the di-methylol ureaether of ethylene glycol mono-methyl ether, and the like.

When employing aqueous solutions of polymerizing material, lowconcentrations are preferred. Ordinarily dilute solutions of suchconcentration that the total weight of resin-forming material is between0.5% and 3%, and the weight of the condensing agent (if used) is between0.01% and 0.15%, Vare used, although solutions more or less concentratedin resin-forming materialy or condensing agent may sometimes bedesirable.

The heat necessary to condition the sheet material for receiving itsfinal moistureproonng coating may be applied in a variety of ways, as,for example, by bringing the cellulosic sheet into contact with heateddrier rolls (or other heated surfaces), or by leading the sheet (or web)through a heated atmosphere in some other manner. The amount of heatrequired to convert the resin-forming material to a substantiallyinsoluble resin varies with the individual resin and the catalyst orother component of the sub-coating composition. A temperature of muchhigher than C., even as high as 180 C., can be applied for a very briefinterval to a regenerated cellulosic sheet wet with an aqueous solutionof polymerizable material to bring about the formation of the desiredsubstantially insoluble polymerization product without damaging thecellulosic sheet. It is usually' desirable to effect the formation ofthe resin in a comparatively brief period, but it is possible to Varythe time (as well as the temperature) rather widely to suit therequirements of special resins and resin combinations Withoutunfavorably affecting the quality of the cellulosic sheet. Temperaturesvery much-under 100V C., sometimes as low as 60 to r10" C., are oftensuicient (and desirable) to cause resin formation in or on the sheetwhen a period of time from 5 to 30 minutes is employed. In the preferredprocedure for applying the aqueous solution of the polymerizablematerial to the cellulosic sheet, the application is made directly onthe casting machine while the cellulosic'sheet is still in gel form.This can be done conveniently by dissolving the resin producing materialin the desired amount directly in the bath commonly used to provide asoftening treatment (i. e., thebath containing the aqueous solution ofglycerin or corresponding material), passing the gel web through thesaid bath in the usual way, and subsequently drying the film in anydesired manner. The resulting sheet is then coated with themoistureproofing surface coat of the desired composition and in thedesired manner.

When applying the anchoring under-coat from an organic solvent solution,the ether material is preferably of a type which will polymerize orharden completely to a tack-free, substantially insoluble state inextremely thin coatings (preferably less than 0.0001 of an inch inthickness), in a period of a few minutes at an elevated temperature(preferably not exceeding C.) It is desirable that the period be 5minutes or less at a temperature of between '70 and 110 C.

As was the case with the materials applied from aqueous solutions, thedifferent polymerization products require different conditions, and thetime and temperature may, therefore, be varied according to the natureof the particular polymeriziation product and catalyst used. Forexample, a longer time at a lower temperature may be employed to effectthe desired result with a given polymerization product which in ashorter time would require a much higher temperature. This principleapplies to the hardening either in the presence or absence of acatalyst, it being understood that any of the well known catalysts whichare soluble in the solvents employed may be used to accelerate theconversion 2o the nal hardened, substantially insoluble aasoaspreferred. It is often possible to use polymerization products which arecommonly regarded as somewhat brittle, since for the purpose of thisinvention they are applied in extremely thin layers which flex with thebase sheet.` `'I'hicker layers, for example, those on the order ofseveral ten-thousandths of an inch in thickness, would crack visibly ifsharply bent. The undercoat is usually extremely thin, being often asthin as 0.00001 to 0.00003 of an inch in thickness, so

that the thickness of the resin coated cellulosc sheet is notappreciably greater than that of the original sheet.

Such organic liquids (solvents) as acetone, ethanol, butanol,iso-butanol, ethyl acetate, benzene, toluene, amyl acetate and the like,and mixtures thereof, are suitable for the formation of solutions of theurea ether material. The consistency of such solutions is governed bythe apparatus employed, the thickness of the coating desired, theconvenience of the operator, and similar factors. Solutions containingbetween 1% and of solids have been found very convenient for obtainingunder-coats of the requisite thickness.

Application of the organic liquid resin solution to the cellulosic sheetmay be made by any of the usual methods, as for example, by immersingthe sheet in the solution, brushing a solution on the sheet, sprayingthe solution on the sheet, or other convenient means. After applicationof the under-coating composition it may be smoothed and the excessremoved in any suitable manner.

In some cases it is highly desirable, and frequently superior resultsmay be obtained, by carrying out the coating process in such a way thatthe anchoring media (polymerizationproducts) will not form a hardened,insoluble, non-tacky surface at once. The incorporation of a cellulosederivative in the under-coating composition, in such proportions that itexudes upon removal o f the organic solvent to form a superficialcoating; enables theweb or sheet to be rolled up for storage prior tofurther treatment. The exuded material, as will be clear from ExamplesVI, VII, VIII and IX, forms a temporary non-tacky surface. Adherence ofadjacent layers of lm bearing its anchor coat is prevented, and whatwould otherwise be a severe' handicap in'handling is removed.

In this modification of the invention, nitrocellulose or a similarcellulose derivative is added to the organic solvent solution of theurea ether material. The solvents (organicliquids) are so selected, andthe concentrations and proportions of the various constituents of thesolution so adjusted, that upon the evaporation of the solvent theethermaterial is substantially all deposited before any great proportionof the cellulose derivative is precipitated. Thereafter, upon completionof the evaporation of the solvent, a deposit or surface layer of thecellulose derivative results. This adequately protects the tacky ethermaterial from adhering to adjacent surfaces when the web is rolled orstacked upon itself, or when in subsequent treatment it comes in contactwith apparatus surfaces such as drier members. and the like. By formingthe superficial, nontacky layer of exuded material it is necessary toheat the anchoring coat only to the extent required for solvent removal,and the heat necessary to produce polymerization and hardening of theinsoluble non-tacky form can be dispensed with.

The resinous materials especially suitable for this type of applicationare the ether type derivatives formed from di-methylol urea in thepresence of alcohols such as propyl, butyl, isobutyl, hexyl, lauryl. andthe like. These'are soluble in organic solvents and can, if desired, bepolymerized further during the drying process. In order to savetime incompleting polymerization after application as an anchoring coat, it isdesirable to use incompletely polymerized resinous material rather thanthe monomeric crystalline monohydric alcoholic ether of methylol urea.

These compounds are preferred because they are tacky, soft, and posses ahigh degree of flexibility `even when applied in fairly thick layers (onthe order of several thousandths of an inch thick). 'I'hese materialscan be applied in extremely thin layers (even as thin as 0.0000I to0.00003 of an inch in thickness), and such embodiments are not excludedfrom the scope of the present invention.

The application of the under-coating compositions containing a cellulosederivative is generally the same as for the other organic liquidsolutions of the urea ether material, so far as the concentration of thecoating composition and the handling of the web during coating isconcerned. The same solventsfor the urea ether material, namely, thealiphatic,cyclic, aromatic and chlorinated hydrocarbons, may be employedwhether the cellulose derivative is present or not.

Although cellulose nitrate is the most readily available andthe mostsatisfactory of the cellulose derivatives so far found for use inconjunction with the undercoating compositions, other types ofderivatives such as cellulose acetate and ethyl cellulose give verysatisfactory results.

Whatever the mode of application, it is preferable that the urea ethermaterial be substantially colorless in lms of several ten-thousandths ofan inch thickness or less. The urea ether material should also besubstantially odorless after being hardened (condensed, polymerized).

If for any reason it is desired to modify the characteristics ofanyspecinc urea ether resin y or of the anchoring under-coat which saidether I with the other ingredients during the preparation of the resinitself or by addition to the solution of said resin in organic solventsafter it has reached the lpartially condensed, polymerized or hardenedstage and is ready for application to the cellulosicsheet. Since theanchoring coat comprises essentially urea formaldehyde monohydricalcohol reaction product the anchoring effectdefinvitely depends uponthe completion of the condensation, polymerization or hardening ofthepartially condensed, polymerlzed or hardened methylol urea ether tothe nal tack-free, substantially yinsoluble y form on the cellulosicsheet, regardless ofthe presence of other materials. In the preferredprocedures an acidic condens- `ing agent is employed in conjunction withthe methylol urea ethers. In general such materials are more effectivethe lower the pH of their solution. Acidic condensing agents for thepolymerization processes of the present invention are well known in theart, and include acids such as phosphoric, maleic. citric, lactic,acidic, trlchloracetic, tartaric, oxalic, phthallc and the like. Acidesters and half esters and the like such as mono-isobutyl phosphate (andgenerically acid esters lof phosphoric acid), dibutyl phosphate,monophenyl phosphate, monobutyl phthalate and mono-ethyl succinate, aresatisfactory condensingagents, as are acid resins such as rosin andthelike. Shellac, alkyd resins and the like may also be used.

The solvents employed for the surface (moistureprooilng) coating shouldbe solvents forI the exuded nitrocellulose which is deposited as asuperficial layer upon this anchoring coating, and the constituents ofthe surface coating should be so adjusted that the addition of thesupercial cellulose derivative coating already present upon the surfaceof the anchoring coating will blend with the other constituents of thesurface coating applied to give a flnal coating of vsuitabletransparency, flexibility, moistureproofness or other desiredcharacteristic.

Moistureproofness, moistureproong and moistureproof materials andexpressions, are defined in United States Patent No. 2,147,180 (Ubben).In the interest of brevity the definitions are not repeated here. Theterms and expressions related thereto and employed herein are used inaccqrdance with such definitions.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is" to beunderstood that this invention is not limited to the specic embodimentsthereof except as defined in the appended claims.

I claim:

1. The process which comprises coating sheet regenerated cellulose witha methylol urea ether resin, and thereafter applying a top coat of amoistureprooflng coating composition.

2. A moistureproof regenerated cellulose sheet wrapping material havinga moistureproofing top coating anchored with an under-coating of a tmethylol urea ether resin.

Per cent Incompletely polymerized isobutyl ether of dimethylol urea 4.0p-Toluene sulfonic acid 0.5 Nitrocellulose (high viscosity) 0.5 Isobutylalcohol r 33.25 Ethyl acetate 33.25 Toluene 28z50 maintaining the sheetat about C. until the coating becomes tack-free, and then top-coatingthe same with a moistureprooflng coating composition.

4. The process which comprises coating a 'softened regenerated cellulosesheet with a composition consisting of:

' Per cent Incompletely polymerized isobutyl ether of dimethylol ureap-Toluene sulfonic acid Nitrocellulose (high viscosity)r 0.5 Isobutylalcohol 33.25 Ethyl acetate 33.25 Toluene .28.50

maintaining the sheet at about 80 C. until-the coating becomestack-free, and then top-coating the same with a moistureprooflng coatinghaving the composition:

Per cent 12.5% N2 nitrocellulose, l0 visc 6.70. Parafhn wax (M. P. 60C.) l .15 Dibutyl phthalate 2.90 lDamar 1.50 Ethyl alcohol '2.90 Acetone1-.45 Water 0.30 Ethyl acetate 51.00 Toluene 33;10

5. The process which comprises coating sheet regenerated cellulose witha methylol urea ether resin, and thereafter applying a top coat of amoistureproong coating having the composition:

6. The process which comprises coating regenerated cellulose sheet witha methylol urea ether, polymerizing the coated material, and thereaftermoistureprooflng thev sheet material by applying a moistureproongcoating composition to the polymerized ether material.

WALTER J. JEBENS.

